A vertical lift module (VLM) is a fully enclosed automated storage and retrieval system that holds inventory on trays in two vertical columns flanking a central extractor, then delivers the requested tray to a fixed access window at operator height [S3][S4].
Because the store grows upward rather than outward, vendors and integrators consistently report floor-area reductions in the 75–90% band when a VLM replaces static shelving: Kardex cites 75% or more [S2], White Systems cites 80–85% [S3], Modula cites up to 90% [S1], and SSI Schaefer's LOGIMAT literature cites up to 90% [S4]. The number a buyer actually achieves depends on what the VLM is replacing and how high the facility ceiling is.
Operating principle: goods-to-person at a single window
A VLM runs on the goods-to-person principle: the operator stays at a fixed picking window and the machine brings the tray to them, rather than the picker walking the aisle [S3][S4]. Inside the enclosure, two columns of trays sit on either side of a central lift; when a SKU is requested at the console or via the WMS, the extractor indexes vertically, engages the correct tray, and rotates it into the access opening [S4][S5].
ICAM's SILO² illustrates the geometry: a multi-column store of 2–7 columns reaching up to 15 m in height, with around 120 tray sizes offered and per-tray payload up to 400 kg [S5]. Modula publishes a more conservative top-of-range payload of 2,200 lb (≈1,000 kg) on its heavy-duty module, with heights spanning 10'10" to 68'11" [S1]. The through-air height-measurement loop that lets the extractor park the next tray a few centimetres above the one below is the same mechanism that drives dynamic slotting on fast-moving SKUs.
Floor-space numbers by ceiling height
Kardex publishes a direct shelving-to-VLM substitution table: a 20 ft (≈6.1 m) ceiling eliminates 45–49 shelving sections and saves roughly 83% of the floor; a 25 ft (≈7.6 m) ceiling eliminates up to 65 sections and reclaims more than 600 ft² (≈56 m²); a 40 ft (≈12.2 m) ceiling eliminates up to 100 sections and returns nearly 1,000 ft² (≈93 m²) [S2]. In every case the recovered floor is sized for the rack footprint that was removed, not for the VLM's own footprint, which is why the headline number tracks ceiling height almost linearly.
The structural reason is that conventional racks store horizontally. In a 25 ft building with 12 ft racks, roughly half of the building's vertical cube is empty airspace above the shelves [S2]. A VLM converts that airspace into active storage, so the savings scale with the height the building already has rather than with how many SKUs you run.
Throughput, payload, and height ranges by vendor
Published VLM throughput and capacity vary widely by product line, and buyers should size to their own SKU profile rather than to the headline number: [S2]
Modula's standard lift module is rated at up to 140 trays/hour with a 2,200 lb (≈1,000 kg) per-tray payload, in unit heights from 10'10" to 68'11" (≈3.3–21.0 m), and bay heights of 27.36", 35.23" or 50.98" (695/895/1,295 mm) [S1]. Modula's Flexibox bin-handling module is rated at up to 180 bins/hour [S1]. The Modula Slim module is designed for tight aisles, with a 66 in (1.6 m) depth and 240 V single-phase or three-phase power [S1]. ICAM's SILO² is documented at up to 400 kg per tray in a 2–7 column, up to 15 m tall configuration [S5]. The Modula Pallet module adds a side window and ground-level handling so no forklift is needed to stage pallets, in heights from 14'7" to 52'10" [S1].
Typical industry cycle times are in the seconds-to-tens-of-seconds range per tray; ICAM states that a SILO² can hand a 400 kg tray to the operator in under a minute [S5]. Modula cites an 85% productivity uplift for vertical storage solutions in general [S1]; treat that as a class-level figure rather than a guaranteed number for any specific install.
VLM vs vertical carousel vs AS/RS stacker crane
VLMs, vertical carousels, and mini-load stacker-crane AS/RS are all goods-to-person systems, but they fit different SKU and building profiles: [S4]
VLM: trays move vertically inside a fixed column and present at a single access window. Best for dense mixed-SKU storage with variable item sizes, tall and narrow footprint, suits a wall or dedicated bay [S4]. Vertical carousel: shelves rotate around a fixed track and present at a single fixed-height opening. Best for high-frequency picking of smaller, uniform items, with a round or oval footprint that needs clearance on all sides [S4]. Stacker-crane AS/RS: a crane runs in an aisle between rack structures, typically at much larger building scale and higher throughput, and is usually specified as part of a wider ASRS system rather than as a stand-alone cell [S5].
The selection heuristic: specify a VLM when SKU sizes vary widely and floor footprint is the binding constraint; specify a carousel when items are uniform and pick frequency is very high; specify a stacker-crane AS/RS when the throughput target and building size justify the aisle and the structural investment [S4][S5].
Selection criteria: who a VLM is for, and who it is not for
A VLM fits operations where small parts, tools, MRO items, electronics components, fasteners, or pharmaceuticals make up a large share of the SKU count and the building is short on floor but has usable ceiling height [S1][S3][S5]. It also fits clean and secure storage needs, because the enclosure keeps stock dust-free and access-controlled, which is one reason healthcare, lab, and aerospace buyers appear in the case-study base [S3].
A VLM is a poor fit where SKUs are pallet-sized and dense, where pick faces are required at multiple heights, or where the building ceiling is too low to make the substitution economic; in those cases, drive-in rack, pallet flow, or a horizontal conveyor sorting line is a better match. Buyers should also confirm that the floor can carry the unit's dead load plus live load at the proposed height, and that the ceiling clearance plus service envelope above the unit is available.
Integration: bays, software, and access
Access geometry is a real engineering decision, not a marketing line. Modula offers internal or external bays, single or dual delivery, with up to three bays on the front, rear, or on multiple floors [S1]. The optional LogiPointer laser on the LOGIMAT marks the exact pick location on the tray, and LogiDual stages the next tray while the current one is still at the window, which cuts wait time between picks [S4]. The optional LogiWork feature adjusts the delivery height per operator, which addresses the ergonomic point that drives most VLM labour-claim numbers [S4].
Software is what turns a VLM from a box into a storage system. Modula's Copilot controller is a 10.4" touch console that takes a barcode scan or manual pick, and integrates with WMS/ERP so that the request arrives automatically [S1][S4]. White Systems pairs its VLM line with MILO inventory management software [S3]. ICAM's WMS interface handles the slotting decision that keeps fast-movers near the window [S5].
Limits, failure modes, and what to verify on site
VLMs are not magic. The 85–90% headline is a replacement figure, not a general floor-area reduction; if the application is already served by high-density racking, the incremental gain is much smaller. The mechanical envelope has to fit the building: a 15 m SILO² [S5] or a 68'11" Modula unit [S1] needs matching ceiling height plus a service envelope above, and the floor must be rated for the concentrated live load. Power is single-phase or three-phase 240 V on lighter Modula units, with 48 V three-phase on the Slim module [S1]; a 400 kg tray cycle on a multi-column store draws meaningful current, so the electrical room and cable run should be sized with the vendor's nameplate, not estimated. Finally, throughput is sensitive to SKU mix: a VLM optimised for mixed-SKU storage with variable item sizes [S4] will not match a carousel's per-second cycle on a uniform small-item pick profile.
Two trackable signals for the rest of 2026: vendors will continue to push the heavier-payload and multi-column configurations (ICAM's 7-column, 15 m SILO² envelope is the current published upper bound [S5]), and integrators are pairing VLMs with AGV robot and AMR robot top-up loops to extend goods-to-person past the VLM's own window. For a deeper look at the dual-mast mechanism that holds the 1,000+ kg class, see the engineering breakdown of single-mast vs twin-mast extractors.